The present invention relates generally to a method and apparatus for generating ultrashort light pulses and more particularly to a method and apparatus for generating ultrashort light pulses which is based on self phase modulation (SPM).
High-power ultrashort laser light pulses propagating in a condensed medium can experience self-phase modulation (SPM) which can lead to the generation of a broadband light continuum. Recent theoretical analyses have concluded that the Stokes and anti-Stokes shifts should appear in the leading and trailing edge of the pump pulse, respectively. This result has been supported by experimental studies where the temporal location of various parts of the continuum was determined using the autocorrelation and streak camera methods in both the femtosecond and picosecond regimes.
In an article entitled Optical Pulse Narrowing By Spectral Windowing of Self Phase Modulated Picosecond Pulses by A. S. L. Gomes etc. appearing in Opt. Commun. 59, 399 (1986) there is disclosed a pulse compression technique based on the spectral temporal distribution of an SPM spectrally broadened pulse in a fiber. According to the article, since the Stokes and anti-Stokes shifts are proportional to the intensity gradients on the sides of the pulse, a window within the broadened spectral profile should eliminate the wings of the generated pulse where the high and low-frequency components are located. A threefold shortening of 80 ps pulses to 30 ps from a Nd:YAG laser broadened from 0.3 to 4 A after propagation through 125 m of optical fiber with a monochromator as a spectral window is described in the article.
In an article entitled Supercontinuum Pulse Generation and propogation in liquid Carbontebachloride by P. P. Ho etc. appl. Opt 26, 2700 (1987), there is described an experiment where the continuum generated in CCl.sub.4 by a weakly focused 8 ps laser pulse was measured by a 2 ps resolution streak camera at several wavelengths. The continuum was found to have a shorter duration than the pump (6 ps) and to be generated over a local spatial domain in the liquid cell.
It is an object of this invention to provide a method and apparatus for generating ultrashort light pulses.
It is another object of this invention to provide an apparatus for generating ultrashort light pulses which is tunable.